This invention relates to a printing plate for all-over printing of large areas by the intaglio printing process, to a method for producing the printing plate, and to a data carrier with a large-area printed image produced by the intaglio printing process.
In line intaglio, flat representations are known to be produced by closely adjacent engraved lines, the individual engraved lines normally being fractions of a millimeter wide and separated from each other by unengraved lands.
For the printing operation the engraved lines of the printing plate are filled with ink. Surplus ink is removed from the printing plate with the aid of a wiping cylinder or doctor blade such that the engraved lines are filled with ink up to the edge. The lands separating the engraved lines are cleaned in this operation at the same time.
During printing, finally, the data carrier to be printed, generally paper, is pressed onto the printing plate under high pressure by means of a pressure cylinder having an elastic surface. The data carrier is thereby pressed into the ink-filled engraved lines of the printing plate, thereby coming in contact with the ink. When the data carrier is detached it draws the ink out of the depressions of the engraved lines. The resulting printed image has printed lines which vary in ink layer thickness depending on the depth of the engraving.
If one uses translucent inks in line intaglio one obtains light tones when printing a white data carrier with low ink layer thicknesses, and darker tones when printing with thick ink layers.
In comparison with other common printing processes, the intaglio printing process can produce printed images with very great ink layer thicknesses. The resulting printed images are even perceptible manually if the engravings are deep enough. By using accordingly fine engravings, however, one can also obtain extremely fine and sharp printed lines.
Although the intaglio printing process can produce very high-quality printed images resolved into line structures, it has the disadvantage of not being able to produce large continuous printed areas, i.e. lines with a width of about one millimeter and more. This is because when the inked printing plate is wiped, not only the surplus ink is removed in the area of large-area engravings but also ink from the engraving. This lowers the ink surface below the surface level of the printing plate in said engraved areas. Since the paper pressed into the engraved areas of the printing plate does not reach the ink surface in all places, gaps arise in the printed image which render the print useless.